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Q. When photons of energy $hv$ fall on a metal plate of work function $'W_0'$, photoelectrons of maximum kinetic energy $'K'$ are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be

MHT CETMHT CET 2019Dual Nature of Radiation and Matter

Solution:

Given, energy of photon $=h v$,
work function $=W_{0}$
and maximum kinetic energy $=K$
So, from the Einstein's photoelectric equation,
$E=K+W_{0} \Rightarrow h v=K+W_{0}$
$\Rightarrow K=h v-W_{0}$...(i)
If frequency of the radiation is doubled, then Einstein's photoelectric equation changed as
$K'=h(2 v)-W_{0}$...(ii)
By substracting the Eq. (i) from (ii), we get
$K'-K=h(2 v)-h v-W_{0}+W_{0}$
$\Rightarrow K'=K+ h v$
So, option (b) is correct.